EDiR cheat sheet

Solitary solid pulmonary nodule 6–8 mm in a patient with risk factors: follow-up CT at 6–12 months, then consider 18–24 months; nodules ≥8 mm: PET-CT, tissue sampling or dedicated follow-up.

Subsolid nodule: pure ground-glass ≥6 mm → CT at 6–12 months then every 2 years to 5 years; part-solid with a solid component ≥8 mm → biopsy or resection.

Pulmonary embolism: CTPA is first line; a right-ventricle/left-ventricle diameter ratio >1.0 with septal bowing indicates right heart strain.

Age-adjusted D-dimer threshold = age × 10 µg/L (FEU) in patients over 50 years with low or intermediate pretest probability.

Stanford A dissection (ascending aorta involved) is a surgical emergency; Stanford B (descending aorta only) is managed medically or endovascularly.

Late gadolinium enhancement: subendocardial = ischaemic; mid-wall = dilated cardiomyopathy or myocarditis; epicardial = myocarditis or sarcoidosis.

Centrilobular emphysema predominates in the upper lobes (smoking); panlobular emphysema predominates in the lower lobes (alpha-1 antitrypsin deficiency).

Cardiothoracic ratio >0.5 on an erect PA chest radiograph indicates cardiomegaly; the ratio is unreliable on AP or supine films.

Coronary artery calcium score >400 denotes high cardiovascular risk and warrants aggressive risk-factor modification.

LI-RADS 5: an observation ≥10 mm in a cirrhotic liver with arterial phase hyperenhancement plus washout, an enhancing capsule, or threshold growth.

Liver haemangioma: peripheral nodular discontinuous enhancement with centripetal fill-in and isointensity to blood pool on delayed phases.

Focal nodular hyperplasia: intense homogeneous arterial enhancement with a central scar, becoming isointense to liver on portal venous phase.

Acute appendicitis on CT: appendix diameter >6 mm, wall enhancement and periappendiceal fat stranding.

Acute cholecystitis: gallbladder wall >3 mm, pericholecystic fluid, distension and a sonographic Murphy sign.

Mechanical small bowel obstruction: dilated loops >3 cm with a transition point and collapsed distal bowel.

Hepatic steatosis: liver attenuation <40 HU on unenhanced CT, or a liver-to-spleen attenuation ratio <0.8.

Double duct sign (dilated common bile duct plus pancreatic duct) suggests a pancreatic head or ampullary tumour.

Crohn disease shows transmural inflammation, skip lesions and fistulae; ulcerative colitis is continuous from the rectum.

Bosniak I: simple cyst, no follow-up; II: a few thin septa, no follow-up; IIF: minimally complex, follow-up imaging; III: indeterminate, surgery or biopsy; IV: enhancing solid or nodular, surgery.

An adrenal mass measuring <10 HU on unenhanced CT is a lipid-rich adenoma and needs no further imaging.

Testicular torsion: absent or reduced Doppler flow with a whirlpool sign of the spermatic cord - a surgical emergency; do not delay surgery for imaging when suspicion is high.

PI-RADS: 1–2 clinically significant cancer unlikely; 3 equivocal; 4–5 likely or highly likely, with targeted biopsy indicated.

Most prostate cancers arise in the peripheral zone, appearing as focal T2 hypointensity with restricted diffusion.

Renal cell carcinoma subtypes: clear cell is hypervascular, papillary is hypovascular, chromophobe shows a spoke-wheel enhancement pattern.

Hydronephrosis with a dilated ureter localises obstruction distal to the pelviureteric junction.

Epiphyseal lesions: chondroblastoma (child), giant cell tumour (adult with closed physis); metaphyseal: osteosarcoma, chondrosarcoma; diaphyseal: Ewing sarcoma, lymphoma.

Aggressive periosteal reaction (sunburst, Codman triangle, hair-on-end) indicates a rapidly growing process such as osteosarcoma or infection.

DXA: T-score ≤ −2.5 = osteoporosis; −1.0 to −2.5 = osteopenia; each 1 SD fall roughly doubles fracture risk.

Osteoarthritis: asymmetric joint space narrowing, osteophytes, subchondral sclerosis and cysts; rheumatoid arthritis: symmetric marginal erosions at MCP/PIP joints with periarticular osteopenia.

Sacroiliitis is detected earliest on MRI as subchondral bone marrow oedema on fluid-sensitive sequences, before radiographic change.

Rotator cuff tears most often involve the supraspinatus tendon at the greater tuberosity, shown by a fluid-signal gap.

Plain radiographs in acute osteomyelitis are normal for 10–14 days; MRI shows marrow oedema within 1–2 days.

The medial meniscus is injured more often than the lateral; a displaced fragment (parrot-beak) indicates a bucket-handle tear.

Extradural haematoma is biconvex and does not cross sutures; subdural haematoma is crescentic, crosses sutures and does not cross the midline.

Acute ischaemic stroke: hyperdense vessel sign and loss of grey–white differentiation; ASPECTS ≤6 indicates a large established infarct.

IV thrombolysis window up to 4.5 hours; mechanical thrombectomy up to 6 hours, and up to 24 hours in selected patients with favourable perfusion imaging.

McDonald criteria require lesions disseminated in space (periventricular, cortical/juxtacortical, infratentorial, spinal cord) and in time.

Ring-enhancing lesions: glioblastoma (thick irregular wall), abscess (thin smooth wall with centrally restricted diffusion), metastasis, toxoplasmosis (basal ganglia).

Vestibular schwannoma: cerebellopontine angle mass widening the internal acoustic meatus with 'ice-cream cone' extension into the canal.

Pituitary macroadenoma >10 mm may show a snowman configuration as it constricts at the diaphragma sellae.

Thyroid nodules are risk-stratified by TIRADS using composition, echogenicity, shape, margin and echogenic foci.

BI-RADS: 0 incomplete; 1 negative; 2 benign; 3 probably benign (≤2% malignancy, 6-month follow-up); 4 suspicious (biopsy); 5 highly suggestive of malignancy; 6 known malignancy.

Suspicious calcifications are fine pleomorphic, fine linear or branching - BI-RADS 4 or 5, requiring stereotactic biopsy.

Suspicious mass features: spiculated or indistinct margins, irregular shape and high density.

Breast density categories a–d; extremely dense breasts reduce mammographic sensitivity and may justify supplemental ultrasound or MRI.

MRI has the highest sensitivity for breast cancer but lower specificity; it is used for high-risk screening, implant assessment and staging.

Screening recall rates should stay below about 10%; double reading increases cancer detection.

Calcifications visible only on mammography require stereotactic vacuum-assisted biopsy.

Elbow ossification order (CRITOE): capitellum, radial head, internal epicondyle, trochlea, olecranon, external epicondyle, at roughly 1, 3, 5, 7, 9 and 11 years.

Salter–Harris: I through physis only; II physis and metaphysis; III physis and epiphysis; IV through all; V crush injury.

Pyloric stenosis: muscle thickness ≥3 mm and canal length ≥15 mm in an infant aged 3–6 weeks with non-bilious projectile vomiting.

Intussusception: target or pseudokidney sign on ultrasound, usually ileocolic, reduced with air or hydrostatic enema if there is no peritonitis.

Necrotising enterocolitis: pneumatosis intestinalis and portal venous gas in a preterm infant, correlated with clinical status.

Malrotation on upper GI study: the duodenojejunal junction fails to cross the midline and lies below the duodenal bulb, giving a corkscrew appearance.

Paediatric radiation protection: use the lowest dose that answers the question, collimate tightly, avoid multiphase CT and prefer ultrasound or MRI.

TACE is the standard treatment for intermediate-stage (BCLC B) hepatocellular carcinoma with preserved liver function and no vascular invasion.

TIPS aims for a portosystemic gradient below 12 mmHg; indications include refractory variceal bleeding and diuretic-resistant ascites.

Uterine fibroid embolisation uses bilateral uterine artery particle embolisation; a substantial minority of patients later require reintervention.

Thermal ablation (radiofrequency or microwave) is curative-intent for hepatocellular carcinoma ≤3 cm and ≤3 nodules in patients unfit for surgery.

Peripheral arterial disease is graded by TASC II lesions: A/B favour endovascular treatment, C/D favour surgery.

TICI 2b or 3 denotes successful reperfusion after mechanical thrombectomy.

IVC filters are indicated when anticoagulation is contraindicated or has failed in a patient with acute proximal DVT or PE.

FDG PET/CT in lymphoma: Deauville 1–3 indicates complete metabolic response; 4–5 indicates residual metabolically active disease.

Bone scintigraphy with Tc-99m MDP reflects osteoblastic activity; a superscan shows intense skeletal uptake with absent renal activity.

Ventilation/perfusion scintigraphy is reported with PIOPED criteria; two or more mismatched segmental defects indicate high probability of pulmonary embolism.

Myocardial perfusion SPECT: a stress defect that fills in at rest is reversible and indicates ischaemia; a fixed defect indicates infarction.

Radioiodine (I-131) is used to treat Graves disease, toxic nodules and to ablate thyroid remnants after thyroidectomy.

PSMA PET is more sensitive than FDG for biochemical recurrence of prostate cancer; DOTATATE PET is used for neuroendocrine tumours.

Sentinel node mapping is performed with Tc-99m nanocolloid, with or without blue dye.

Hounsfield units: water 0, air about −1000, fat −50 to −100, soft tissue 20–60, bone above 400.

Effective dose (mSv) = DLP (mGy·cm) × conversion factor k, approximately 0.015 for the abdomen.

Approximate effective doses: chest radiograph 0.02 mSv, head CT 2 mSv, abdominal CT 10 mSv.

Dose limits: occupational 20 mSv per year averaged over 5 years (50 mSv in any single year); public 1 mSv per year.

Dose is roughly proportional to mAs and to the square of kVp; raising kVp reduces contrast but lowers dose for equivalent image noise.

Gadolinium-based agents shorten T1; macrocyclic chelates carry the lowest risk of nephrogenic systemic fibrosis.

Justification and optimisation (ALARA) underpin ICRP principles; CTDIvol and DLP are the standard CT dose descriptors.

Ultrasound safety: thermal index estimates heating and mechanical index estimates cavitation; both should be kept as low as reasonably achievable.